Valve drive of an internal combustion engine

ABSTRACT

A valve drive ( 1, 1′ ) of an internal combustion engine with stroke-variable gas-exchange valve activation is provided. The valve drive includes a camshaft ( 2, 2′ ) with a carrier shaft ( 3 ) and a cam piece ( 4, 4′ ) that is arranged in a rotationally locked way on the carrier shaft and that can move between axial positions and that has a cam group of directly adjacent cams ( 14   a - c,    15   a - c ) with different lobes and a groove-shaped axial link ( 16, 16′ ) and an activation element ( 18, 19 ) that can be coupled in the axial link for shifting the cam piece on the carrier shaft. The cam piece is provided with a bearing journal ( 12, 13,  or  12′ ) on which the camshaft is supported in the radial direction at a camshaft bearing point ( 9, 10,  or  9′ ) of the internal combustion engine. Here, the axial link is constructed overlapping with the camshaft bearing point on the bearing journal in the axial direction, and the activation element runs in the camshaft bearing point.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of German Patent Application No. 10 2009 016 463.4, filed Apr. 4, 2009, which is incorporated herein by reference as if fully set forth.

1. Field of the Invention

The invention relates to a valve drive of an internal combustion engine with stroke-variable gas-exchange valve activation. The valve drive comprises a camshaft with a carrier shaft and a cam piece that is arranged in a rotationally locked manner on the carrier shaft and that can move between axial positions and that has a cam group of directly adjacent cams with different lobes and a groove-shaped axial link extending on the outer periphery and an activation element that can be coupled in the axial link for shifting the cam piece on the carrier shaft. The cam piece is provided with a bearing journal on which the camshaft is supported in the radial direction at a camshaft bearing point of the internal combustion engine.

2. Background of the Invention

The stroke variability of such a valve drive is based in a known way on a cam piece with cams that are directly arranged on this cam piece and whose different lobes are transferred selectively onto a gas-exchange valve by a conventional, rigidly constructed cam follower. For the operating-point-dependent activation of each lobe, the cam piece is arranged on a carrier shaft in a rotationally locked way but can move between two or more axial positions and has axial connecting paths running in the opposite sense in the form of spiral grooves. The shifting of the cam piece is realized according to the construction of the connecting paths by one or more activation elements that are coupled selectively in the spiral grooves. The axial profile of the spiral groove engaged with the activation element has the result that, during the common (lobe-free) base-circle phase of the cam of a cam group, the cam piece is shifted in a self-controlled and camshaft-angle-true way from one axial position to the next. The radial profile of one spiral groove is usually shaped so that this becomes increasingly flatter at the end of a shifting process and shifts the currently engaged activation element into its disengaged rest position.

Among other things, a valve drive according to the class with two-stage stroke variability emerges from DE 101 48 179 A1. One essential property of this valve drive is that the individual cam pieces are provided with bearing journals that are supported in a sliding manner both in the radial and also axial directions at associated camshaft bearing points of the internal combustion engine. Accordingly, the camshaft bearing of the valve drives disclosed in DE 101 48 177 A1 and DE 10 2004 022 832 A1 is realized directly on the carrier shafts. In this case, while the length of a cam piece is definitely defined by the number of cams and the connecting paths, as well as their spatial arrangement relative to each other, in the first case, the length of the bearing journal or possibly the length of the bearing journals is also to be taken into account. Under consideration of various structural parameters of the internal combustion engine, in particular, the cylinder and gas-exchange valve spacing, the number and width of the cams, and also the middle or end camshaft bearing position with respect to a cylinder, however, the required length of the cam piece quickly conflicts with the installation space available for this piece. This applies to an elevated degree for three-stage stroke variability.

SUMMARY

Therefore, the present invention is based on the objective of refining a valve drive of the type named above so that the cam piece is constructed with the most compact possible structure in the axial direction, so that the valve drive not only can be used widely also in small-volume internal combustion engines, but there is also a high potential for stroke variability with more than two stages, in particular, three stages.

The objective is met with the arrangement according to the invention, while advantageous refinements and constructions of the invention are also provided. Accordingly, the axial link should be constructed overlapping with the camshaft bearing point on the bearing journal in the axial direction, wherein the activation element runs in the camshaft bearing point. In other words, the idea forming the basis of the invention provides that the spatial separation of the bearing journal and axial link is to be eliminated and these are to be “fused” with each other in the axial direction, in order to be able to reduce the axial structural space of the cam piece accordingly and/or in order to be able to provide the cam group with an additional cam.

With respect to the stability and durability of the camshaft bearing, which is obviously still to be guaranteed, in one refinement of the invention it is provided that the bearing journal with the camshaft bearing point forms a sliding bearing, wherein the bearing journal has sliding surface sections on both sides of the axial link in the axial direction.

In addition, the bearing diameter of the bearing journal should be larger than the surrounding diameter of the cam lying closest to the bearing journal, wherein this cam and the camshaft bearing point overlap in the axial direction in one of the axial positions of the cam piece. The insertion of the cam group made possible in this manner into the camshaft bearing point is especially preferred or even necessary when the cam piece has two cam groups for activating two gas-exchange valves that are arranged with a small spacing relative to the camshaft bearing point and when, in addition, a three-stage stroke variability is provided with three cams for each cam group.

With respect to the bearing arrangement of the camshaft, the cam piece should have two bearing journals constructed on its axial end sections and two cam groups arranged between the bearing journals. This bearing arrangement correlates with camshaft bearing points that are arranged between the cylinders of an internal combustion engine with multi-valve technology. Unidirectional axial links with a single connecting path according to DE 101 48 179 A1 cited above could be provided on both bearing journals in which activation elements running in both associated camshaft bearing points can be coupled.

In an alternative construction of the invention hereto, the cam piece should have two cam groups constructed on its axial end sections and only one bearing journal arranged between the cam groups. This bearing arrangement correlates with camshaft bearing points that are arranged between the gas-exchange valves of a cylinder of an internal combustion engine with multi-valve technology.

In addition, it is provided that the cam piece has exactly one axial link that has a bidirectional construction with two connecting paths running in the opposite sense in the axial direction. One construction of such an axial link is already known from DE 101 48 177 A1 cited above: here the two connecting paths are arranged one next to the other in the peripheral direction of the bearing journal and cross in their middle. The essential advantage relative to the spatially separated, unidirectional connecting paths consists, on one hand, in the comparatively small, axial structural space requirements for the axial link and, on the other hand, in that a single activation element is sufficient for both directions of movement.

This also applies for a bidirectional axial link according to an alternative second construction. In this case, the two connecting paths should be arranged one behind the other in the peripheral direction of the bearing journal, wherein each starting point of one of the connecting paths is adjacent to the end point of the other connecting path. The kinematics of such an axial link emerges in detail from DE 10 2009 009 080 A1 of the applicant, which is not a prior publication, whose entire contents are incorporated herein by reference as if fully set forth.

In addition, the two constructions named above allow a comparatively easily performed expansion of the stroke variability from two to three stages in that two activation elements are coupled selectively in the bidirectional axial links. This is disclosed in detail in DE 10 2007 051 739 A1 of the applicant, which is also not a prior publication, for the construction with crossing connecting paths. The entire contents of that publication are also incorporated herein by reference as if fully set forth.

In the case of three-stage stroke variability, it is provided that one of the three cams of a cam group is free of lobes. This cam involves a so-called base-circle cam that leads to the shutdown of the gas-exchange valve due to its purely cylindrical shape.

The features and constructions of the invention should also be capable of being combined with each other arbitrarily as far as possible and useful.

BRIEF DESCRIPTION OF THE DRAWINGS

Additional features of the invention emerge in the following description and from the drawings in which embodiments of the invention are shown partially simplified. If not mentioned differently, here identical or functionally identical features or components are provided with identical reference symbols. Shown are:

FIG. 1 is a perspective, assembled view of cutout section of a cylinder head of an internal combustion engine with a first construction of a valve drive according to the invention;

FIG. 2 is the view of FIG. 1 without camshaft bearing cover;

FIG. 3 is a perspective, longitudinal cross-sectional view of the arrangement according to FIGS. 1 and 2;

FIG. 4 is a first perspective view of the axial link according to FIGS. 1 to 3;

FIG. 5 is a second (ca. 180° rotated) perspective view of the axial link according to FIG. 4;

FIG. 6 is perspective view of a cutout section of a cylinder head of an internal combustion engine with a second construction of a valve drive according to the invention;

FIG. 7 is a perspective view of the cutout section from FIG. 6 without the camshaft bearing cover;

FIG. 8 is a perspective, detailed partial view of the cam piece according to FIGS. 6 and 7;

FIG. 9 is a first perspective view of the axial link according to FIGS. 6 to 8;

FIG. 10 is a second (ca. 120° rotated) perspective view of the axial link according to FIG. 9; and

FIG. 11 is a third (ca. 240° rotated) perspective view the axial link according to FIG. 9.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIGS. 1 to 3, a cutout section of a valve drive 1 of an internal combustion engine that is essential for understanding the invention is disclosed with stroke-variable gas-exchange valve activation and four-valve technology. A component that is central to the function of the valve drive 1 is a camshaft 2 that comprises a carrier shaft 3 and also cam pieces 4 that are arranged in a rotationally locked way on the carrier shaft and that can move between three axial positions—corresponding to the number of cylinders of the internal combustion engine. For the purpose of axial shifting, the carrier shaft 3 is provided with outer longitudinal teeth and each cam piece 4 is provided with corresponding inner longitudinal teeth. The teeth 5 and 6 can be seen in FIGS. 3 and 8. The intermediate spaces that can be seen between the axial end sections 7 and 8 allow the separate shifting of the cam pieces 4 in sync with the ignition sequence of the internal combustion engine into an adjacent axial position. The radial bearing of the camshaft 2 is realized in camshaft bearing points 9 and 10 that are arranged, in this embodiment, between the cylinders of the internal combustion engine. The cam followers 11 that can be seen between the camshaft bearing points 9, 10 activate the two intake valves of a cylinder not shown here.

As emerges from FIG. 2—the same cutout section is shown as in FIG. 1, but without the top camshaft bearing cover—the cam piece 4 is provided on its end sections 7, 8 with bearing journals 12 and 13 of different widths that are supported in a sliding way both in the radial and also axial directions on the inner lateral surfaces of the camshaft bearing points 9, 10. Cam groups running between the bearing journals 12, 13 each include three directly adjacent cams 14 a-c and 15 a-c that have different lobes for the same base-circle radius. These are transmitted to the gas-exchange valves by the cam follower 11 selectively, i.e., as a function of the instantaneous axial position of the cam piece 4. The different lobes are to be understood as different magnitudes of each cam stroke and/or different valve control times of the cams 14 a-c and 15 a-c. For example, the cams 14 a and 15 a involve so-called base-circle cams that are free of lobes and that each lead to shutdown of the gas-exchange valve.

The shifting of the cam piece 4 between its axial positions is realized outside of the lobes during the common base-circle angle of the cams 14 a-c and 15 a-c. The functional principle known, in principle, for example, from DE 101 48 179 A1 cited above for the actuator mechanism required here touches upon a groove-shaped axial link 16 on the cam piece 4 and an activation element in the form of a cylindrical actuator pin that is arranged fixed in position in the axial direction relative to the camshaft 2 but can move in the radial direction toward the camshaft 2 in the internal combustion engine and can be coupled in the axial link 16 for the purpose of shifting the cam piece 4.

The current used actuator 17 that can be seen only hidden in FIGS. 1 and 2 emerges more clearly from the longitudinal cutout in FIG. 3. The actuator 17 comprises two actuator pins 18 and 19 that are spaced apart with a cam width and that are driven selectively out from a common actuator housing by an electromagnetically activated locking mechanism and that are alternately coupled in the single axial link 16 for each cam piece 4. The structural configuration of this actuator 17 emerges in detail from DE 10 2009 010 949 A1 of the applicant, which is not a prior publication, whose entire contents are also incorporated herein by reference as if fully set forth.

The axial link 16 shown in FIGS. 4 and 5 as details from two opposite perspective views is constructed with bidirectional action with two connecting paths 20 and 21 running in opposite sense in the axial direction, wherein the two connecting paths 20, 21 are arranged one next to the other in the peripheral direction and cross in their middle. While such an axial link 16 is known in principle, the connecting paths 20, 21 in the present embodiment are offset in height relative to each other in the radial direction, in order to generate two-sided positive guidance of the coupled actuator pin 18 or 19 along the connecting path 20 that is lower in the radial direction. In this way, also for a lower camshaft rotational speed and a correspondingly lower axial mass inertia of the cam piece 4 whose shifting process along the connecting path 20 lower in the radial direction can be completed after passing the crossing point.

Concerning the functioning of the actuator mechanism: coupling of the actuator pin 18 in the connecting path 20 leads to a shift of the cam piece 4 to the left (in FIG. 3) and—starting from its shown axial position in which the cam followers 11 are loaded by the middle cams 14 b and 15 b—to an activation of the cams 14 c and 15 c. Conversely, coupling of the actuator pin 19 in the connecting path 21 leads to a shift of the cam piece 4 to the right and—starting from the shown axial position—to an activation of the cams 14 a and 15 a. Two coupling processes of the same actuator pin 18 or 19 immediately following each other lead to a back and forth shifting of the cam piece 4 into the original axial position. In contrast, alternating coupling processes of the actuator pins 18 and 19 immediately following each other in the same connecting path 20 or 21 leads to a rectified shift of the cam piece 4 about two axial positions. Thus, for setting the three axial positions of the cam piece 4, only one actuator 17 with the two actuator pins 18 and 19 and one axial link 16 are required.

The cam piece 4 is secured against uncontrolled shifting in its axial position by a locking device. The known locking device not shown here in detail comprises a spring-loaded pressure piece 22 that is supported in a cross borehole 23 of the carrier shaft 3 and—according to the axial position of the cam piece 4—engages in one of three peripheral grooves 24, 25, and 26 on the inner periphery of the cam piece 4.

The actuator 17 runs according to the invention within the axial longitudinal extent of the camshaft bearing point 9. This means that its inner lateral surface is cut from a borehole for holding the actuator 17 and the axial link 16 constructed on the periphery of the bearing journal 12 and the camshaft bearing point 9 overlap in the axial direction. Sliding surface sections 27 and 28 on both sides of the axial link 16 are used for forming the sliding bearing of the bearing journal 12 in the camshaft bearing point 9. The bearing journal 13 is constructed significantly more narrowly and as a complete cylinder relative to the bearing journal 12 with the axial link 16 running on this journal.

An alternative construction of a stroke-variable valve drive 1′ emerges from FIGS. 6 to 8, wherein the following statements are largely limited to the structural differences with the valve drive 1. For the valve drive 1′, the camshaft bearing points 9′ are not located between the cylinders, but instead between the gas-exchange valves 29 of a cylinder. Accordingly, the two cam groups with the cams 14 a-c and 15 a-c are arranged on the two end sections 7, 8 of the cam piece 4′ that has only one bearing journal 12′ running in-between for the radial bearing of the camshaft 2′ in the associated camshaft bearing point 9′. The actuator 17 known from FIGS. 1 to 3 is held in this case in the top camshaft bearing cover 30.

Both valve drives 1′ and 1 have in common that the gas-exchange valves 29 and thus also the cam followers 11 run spaced closely apart to the camshaft bearing point or points 9′ or 9 and 10. The axial free travel of the cam groups required for the three-stage stroke variability relative to the camshaft bearing point 9′ is created such that according to the axial position of the cam piece 4′, the cam groups with their cams 14 a and 15 c lying closest to the bearing journal 12′ are inserted into the camshaft bearing point 9′. In the axial position of the cam piece 4′ shown in FIG. 7, the gas-exchange valves 29 are instantaneously loaded by the cams 14 c and 15 c, while the base-circle cam 14 a and the camshaft bearing point 9′ overlap in the axial direction. The opposite axial position of the cam piece 4′ here with the then effective base-circle cams 14 a and 15 a equally requires an insertion of the cam 15 c into the camshaft bearing point 9′.

As is clear in FIG. 8, the axial free travel of the cam groups relative to the camshaft bearing point 9′ is produced structurally such that the bearing diameter of the bearing journal 12′ is larger than the surrounding diameter 31 drawn with dotted lines of the cam 15 c lying closest to the bearing journal 12′ and is also larger than the base-circle diameter of the cam 14 a. This geometric construction occurs with respect to the cams 14 c and 15 a in a corresponding way for the valve drive 1 according to FIGS. 1 to 5.

The axial link 16′ constructed on the periphery of the bearing journal 12′ is likewise constructed with bidirectional action with two connecting paths 20′ and 21′ running in the opposite sense in the axial direction and is limited on both sides by the sliding surface sections 27, 28 that form a sliding bearing with the camshaft bearing point 9′. Relative to the axial link 16, however, the connecting paths 20′, 21′ are not arranged one next to the other with identical starting and end points, but are instead arranged one behind the other in the peripheral direction of the bearing journal 12′. As becomes clear from FIGS. 9 to 11 with an axial link 16′ each rotated by approximately 120°, the starting point 32 of the connecting path 20′ is adjacent to the end point 33 of the connecting path 21′, and the starting point 34 of the connecting path 21′ is adjacent to the end point 35 of the connecting path 20′. Also, in this case, for switching between the three axial positions of the cam piece 4′, two actuator pins 18, 19 spaced apart by a cam width are sufficient (see FIG. 3) that are coupled alternately in this axial link 16′ corresponding to the previous explanation. The camshaft angle available for the shifting of the cam piece 4′ is indeed significantly smaller relative to the axial link 16 with the crossing connecting paths 20, 21, but there is a significant advantage in the continuous positive guidance of each coupled actuator pin 18 or 19, so that secure shifting of the cam piece 4′ is also possible without its supporting mass inertia, i.e., for the smallest camshaft rotational speeds.

LIST OF REFERENCE SYMBOLS

1. Valve drive

2. Camshaft

3. Carrier shaft

4. Cam piece

5. Outer longitudinal teeth

6. Inner longitudinal teeth

7. Axial end section of the cam piece

8. Axial end section of the cam piece

9. Camshaft bearing point

10. Camshaft bearing point

11. Cam follower

12. Bearing journal

13. Bearing journal

14. Cam group with cams 14 a-c

15. Cam group with cams 15 a-c

16. Axial link

17. Actuator

18. Actuator pin/activation element

19. Actuator pin/activation element

20. Connecting path

21. Connecting path

22. Pressure piece

23. Cross borehole of the carrier shaft

24. Circumferential groove

25. Circumferential groove

26. Circumferential groove

27. Sliding surface section

28. Sliding surface section

29. Gas-exchange valve

30. Camshaft bearing cover

31. Surrounding diameter

32. Starting point of one connecting path

33. End point of the other connecting path

34. Starting point of the other connecting path

35. End point of one connecting path 

1. A valve drive of an internal combustion engine with stroke-variable gas-exchange valve activation, comprising a camshaft with a carrier shaft and a cam piece that is arranged in a rotationally locked manner on the carrier shaft and is moveable between axial positions and that has a cam group of directly adjacent cams with different lobes and a groove-shaped axial link, an activation element that is coupleable in the axial link for shifting the cam piece on the carrier shaft, the cam piece is provided with a bearing journal on which the camshaft is supported in a radial direction at a camshaft bearing point of the internal combustion engine, the axial link is constructed overlapping with the camshaft bearing point on the bearing journal in an axial direction, and the activation element runs in the camshaft bearing point.
 2. The valve drive according to claim 1, wherein the bearing journal with the camshaft bearing point forms a sliding bearing, the bearing journal has sliding surface sections on both sides of the axial link in the axial direction.
 3. The valve drive according to claim 1, wherein a bearing diameter of the bearing journal is larger than a surrounding diameter of the cam lying closest to the bearing journal, and the cam lying closet to the bearing journal and the camshaft bearing point overlap in the axial direction in one of the axial positions of the cam piece.
 4. The valve drive according to claim 1, wherein the cam piece has two of the bearing journals that are constructed on axial end sections thereof and two cam groups are arranged between the bearing journals.
 5. The valve drive according to claim 1, wherein the cam piece has two of the cam groups constructed on axial end sections thereof and the bearing journal consists of a single bearing journal arranged between the cam groups.
 6. The valve drive according to claim 1, wherein the cam piece includes a single one of the axial links that is constructed in a bidirectional way with two connecting paths running in an opposite sense in the axial direction.
 7. The valve drive according to claim 6, wherein the two connecting paths are arranged one next to the other in a peripheral direction of the bearing journal and cross one another in a middle area.
 8. The valve drive according to claim 6, wherein the two connecting paths are arranged one behind the other in a peripheral direction of the bearing journal, and each starting point of one of the connecting paths is adjacent to an end point of the other of the connecting paths.
 9. The valve drive according to claim 1, wherein there are three directly adjacent cams for each of the cam groups and two activation elements that are coupleable alternately in the same axial link.
 10. The valve drive according to claim 9, wherein one of the three cams is free of lobes. 